<p>a: Map of Greater Copenhagen Area, divided into parishes with color indicating average number of routers discovered per scan; rectangle overlay indicates the city center. b: The number of access points visible in each scan is correlated with the population density (<i>r</i><sup>2</sup> = 0.5). Even in low population density areas there are several routers visible on average in each scan. Therefore, knowing the positions of only a subset of routers is enough for precise location sensing. c: Distribution of number of routers per scan. In our dataset 92% of scans contain at least one router.</p
